(Background) In an early twentieth-century classroom at Radcliffe College, as at other schools, astronomy came into its own as a viable and important subject.
(Inset A) Harlow Shapley (1885-1972), discovered our place in the "suburbs" of the Milky Way, dispelling the notion that the Sun resides at the center of the universe.
(Inset B) Annie Cannon (1863-1941), one of the greatest astronomical cataloguers of all time, carefully analyzed photographic plates to classify nearly a million stars over the course of fifty years of work at Harvard.
(Inset C) Maria Mitchell (1818-1889) in her observatory on Nantucket Island, made important contributions to several areas of astronomy.
(Inset D) Edwin Hubble (1889-1953), here posing in front of one of the telescopes on Mount Wilson, in California, is often credited with having discovered the expansion of the universe.
LEARNING GOALS
Studying this chapter will enable you to:
Relate how some ancient civilizations attempted to explain the heavens in terms of Earth-centered models of the universe.
Summarize the role of Renaissance science in the history of astronomy.
Explain how the observed motions of the planets led to our modern view of a Sun-centered solar system.
Sketch the major contributions of Galileo and Kepler to the development of our understanding of the solar system.
State Kepler's laws of planetary motion.
Explain how Kepler's laws enable us to construct a scale model of the solar system, and explain the technique used to determine the actual size of the planetary orbits.
State Newton's laws of motion and universal gravitation and explain how they account for Kepler's laws.
Explain how the law of gravitation enables us to measure the masses of astronomical bodies.
Living in the Space Age, we have become accustomed to the modern view of our place in the universe. Images of our planet taken from space leave little doubt that Earth is round, and no one seriously questions the idea that we orbit the Sun. Yet there was a time, not so long ago, when our ancestors maintained that Earth was flat and lay at the center of all things. Our view of the universe? and of ourselves—has undergone a radical transformation since those early days. Earth has become a planet like many others, and humankind has been torn from its throne at the center of the cosmos and relegated to a rather unremarkable position on the periphery of the Milky Way Galaxy. But we have been amply compensated for our loss of prominence—we have gained a wealth of scientific knowledge in the process. The story of how all this came about is the story of the rise of the scientific method and the genesis of modern astronomy.
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